The semiconductor and packaging industries, among others, utilize conventional processes to form thin metal and metal oxide films in their products. Examples of such processes include evaporation, sputter deposition or sputtering, chemical vapor deposition (“CVD”) and thermal oxidation. Evaporation is a process whereby a material to be deposited is heated near the substrate on which deposition is desired. Normally conducted under vacuum conditions, the material to be deposited volatilizes and subsequently condenses on the substrate, resulting in a blanket, or unpatterned, film of the desired material on the substrate. This method has several disadvantages, including the requirement to heat the desired film material to high temperatures and the need for high vacuum conditions. Unless a screen or shadow is employed during evaporation, an unpatterned, blanket film results from this process.
Sputtering is a technique similar to evaporation, in which the process of transferring the material for deposition into the vapor phase is assisted by bombarding that material with incident atoms of sufficient kinetic energy such that particles of the material are dislodged into the vapor phase and subsequently condense onto the substrate. Sputtering suffers from the same disadvantages as evaporation and, additionally, requires equipment and consumables capable of generating incident particles of sufficient kinetic energy to dislodge particles of the deposition material.
CVD is similar to evaporation and sputtering but further requires that the particles being deposited onto the substrate undergo a chemical reaction during the deposition process in order to form a film on the substrate. While the requirement for a chemical reaction distinguishes CVD from evaporation and sputtering, the CVD method still demands the use of sophisticated equipment and extreme conditions of temperature and pressure during film deposition.
Thermal oxidation also employs extreme conditions of temperature and an oxygen atmosphere. In this technique, a blanket layer of an oxidized film on a substrate is produced by oxidizing an unoxidized layer which had previously been deposited on the substrate.
Several existing film deposition methods may be undertaken under conditions of ambient temperature and pressure, including sol-gel and other spin-on methods. In these methods, a solution containing precursor particles that may be subsequently converted to the desired film composition is applied to the substrate. The application of this solution may be accomplished through spin-coating or spin-casting, where the substrate is rotated around an axis while the solution is dropped onto the middle of the substrate. After such application, the coated substrate is subjected to high temperatures which convert the precursor film into a film of the desired material. Thus, these methods do not allow for direct imaging to form patterns of the amorphous film. Instead, they result in blanket, unpatterned films of the desired material. These methods have less stringent equipment requirements than the vapor-phase methods, but still require the application of extreme temperatures to effect conversion of the deposited film to the desired material.
In one method of patterning blanket films, the blanket film is coated (conventionally by spin coating or other solution-based coating method; or by application of a photosensitive dry film) with a photosensitive coating. This photosensitive layer is selectively exposed to light of a specific wavelength through a mask. The exposure changes the solubility of the exposed areas of the photosensitive layer in such a manner that either the exposed or unexposed areas may be selectively removed by use of a developing solution. The remaining material is then used as a pattern transfer medium, or mask, to an etching medium that patterns the film of the desired material. Following this etch step, the remaining (formerly photosensitive) material is removed, and any by-products generated during the etching process are cleaned away if necessary.
In another method of forming patterned films on a substrate, a photosensitive material may be patterned as described above. Following patterning, a conformal blanket of the desired material may be deposited on top of the patterned (formerly photosensitive) material, and then the substrate with the patterned material and the blanket film of the desired material may be exposed to a treatment that attacks the formerly photosensitive material. This treatment removes the remaining formerly photosensitive material and with it portions of the blanket film of desired material on top. In this fashion a patterned film of the desired material results; no etching step is necessary in this “liftoff” process. However, the use of an intermediate pattern transfer medium (photosensitive material) is still required, and this is a disadvantage of this method. It is also known that the “liftoff” method has severe limitations with regard to the resolution (minimum size) that may be determined by the pattern of the desired material. This disadvantage severely limits the usefulness of this method.
It is thus evident that the deposition of blanket films that need subsequently be patterned invokes the need for several extra costly and difficult processing steps.
In yet another method of forming patterned films, a blanket film of desired material may be deposited, e.g., by one of the methods described above, onto a substrate that has previously been patterned, e.g., by an etching process such as the one described previously. The blanket film is deposited in such a way that its thickness fills in and completely covers the existing pattern in the substrate. A portion of the blanket film is then isotropically removed until the remaining desired material and the top of the previously patterned substrate sit at the same height. Thus, the desired material exists in a pattern embedded in the previously patterned substrate. The isotropic removal of the desired material may be accomplished via an etching process; commonly in the case of the formation of semiconductor devices it is envisioned that this removal is effected through a process known as chemical mechanical planarization (“CMP”). This involves the use of a slurry of particles in conjunction with a chemical agent to remove substantial quantities of the desired material through a combination of chemical and mechanical action, leaving behind the desired material in the desired places embedded in the patterned substrate. This method of forming a patterned film demands the use of expensive and complicated planarization equipment and extra consumable materials including planarization pads, slurries and chemical agents. In addition, the use of small slurry particles demands that these particles be subsequently removed from the planarized surface, invoking extra processing steps.
While some of these methods are more equipment-intensive than others and differ in the use of either solution- or vapor-phase methods, such conventional processes for forming metal and metal oxide films is not optimal because, for example, they each require costly equipment, are time consuming, require the use of high temperatures to achieve the desired result, and result in blanket, unpatterned films where, if patterning is needed, further patterning steps are required. Many of these methods suffer the additional disadvantage of, in many cases, forming polycrystalline films which may not be suitable for a variety of applications. A desirable alternative to these methods would be the use of a precursor material that may be applied to a substrate and selectively imaged and patterned to form an amorphous film without the need for intermediate steps.
One use of thin films in semiconductor processing is for the formation of thin top-surface imaging (hereafter “TSI”) layers, typically atop organic layers that have already been applied to the substrate. In this instance, the organic layer need not be photoactive, since the thin film to be deposited will be subsequently patterned using conventional methods. The use of these thin films for TSI confers several process advantages, including resistance to plasma etching not afforded by the use of photoresist masks, and the increased resolution of the lithographic process afforded by a very thin film. Typical thin films for TSI include metal and silicon nitride and oxide films, and a great deal of research has also been conducted on a process known as silylation. This process involves the vapor deposition of a thin film of a silicon-containing species on top of a previously deposited organic layer. This thin film of the silicon species can then be imaged to form a thin film of silicon oxide, which acts as the TSI layer during oxygen-plasma patterning of the organic layer beneath. The acceptance of silylation processes by the semiconductor and packaging industries has been insignificant as a result of a number of process and cost limitations.
In the preparation of a TSI layer a period of time may exist between the deposition of a precursor film and the patterning or exposure of that film. During this time some films lose significant film material through hydrolysis under atmospheric conditions. Another use of thin films in semiconductor processing is for the formation of hard masks, e.g., for use in ion implantation processing. Ion implantation is a well known technique used, for example, in forming doped regions in a substrate during semiconductor fabrication. Ion implantation frequently requires a patterned blocking layer, also known as a hard mask, which directs the ions to be implanted only into predetermined regions. For example, U.S. Pat. No. 5,436,176 to Shimizu et al. discloses, in “Embodiment 1”, maskless implantation of a silicon substrate covered by a silicon oxide film, which is disclosed to be thrice-implanted with boron atoms. Alternatively, the same patent discloses, in “Embodiment 3”, implantation using multiple hard masks in a thrice-repeated method comprising the following sequence of steps: forming a mask on a silicon substrate covered by a silicon oxide film, implantation with phosphorus, forming a second mask, implantation with boron, and, finally, annealing.
As previously discussed, formation of a hard mask by any of these processes requires a relatively large number of processes steps. Eliminating some of these steps before etching or ion implantation would be beneficial because, for example, it would simplify the process used, increase its efficiency and reduce its cost.
One approach to solve the problem involves the use of a photoresist as a mask. However, it is well known that photoresists have low etch resistance to certain plasma etching chemistries, particularly for the patterning of organic layers which may be employed as intermediate protecting layers or which are finding increasing use as low-dielectric constant (“low-k”) dielectrics and low stopping power for ions. Therefore, undesirably thick photoresist films are required to permit complete etching of the layer to be patterned prior to complete erosion of the masking layer or to prevent implantation of the areas of the substrate onto which they are applied. Another disadvantage is that ion implanted photoresist can be exceedingly difficult to remove from a wafer. Other solutions to the problem have been attempted, for example, by first applying a hard mask, then applying a photoresist layer atop the hard mask followed by patterning before etching or ion implantation take place. Combining some of the many steps disclosed in the prior art methods before plasma etching or ion implantation, or even eliminating one or more of them, would help simplify these processes. Thus, a method to eliminate steps in a plasma patterning or an ion implantation process would be highly desirable.
The present processes for metal complex precursor deposition have been developed as less expensive methods of forming metal and metal oxide hard mask films. One embodiment of this process, photochemical metal organic deposition, involves the use of a metal organic for the metal complex precursor and a means for converting the metal organic to the metal or metal oxide film, such as incident radiation or thermal energy. Specifically, in this process, a precursor metal organic is applied to a surface, for example, by dissolving it in a suitable organic solvent to form a precursor solution, which is deposited onto a surface by any known means. The precursor is then at least partially converted to a metal or metal oxide layer by a partial converting means and/or converting means, such as by exposure to an energy source, e.g., light, ion-beam bombardment, electron-beam bombardment, or thermal or heat treatment or annealing. As such, the present processes have utility in, e.g., the semiconductor and packaging industries.
U.S. Pat. No. 5,534,312 to Hill et al. discloses a photoresist-free method for making a patterned, metal-containing material on a substrate which includes the steps of depositing an amorphous film of a metal complex on a surface of a substrate, placing the film in a selected atmosphere, and exposing selected areas of the film to electromagnetic radiation, preferably ultraviolet light and optionally through a mask, to cause the metal complex in the selected areas to undergo a photochemical reaction. However, this reference does not envision use of a patterned, metal-containing material as a hard mask to protect underlying layers from a plasma etching environment.
U.S. Pat. No. 6,071,676 to Thomson et al. discloses that its integrated circuit manufacturing process causes degradation of an applied compound where the compound is contacted by a radiant or particle beam. In other words, the dimensions of the deposit caused by degradation of the compound is proportional to the focal width of the irradiating beam. Nanoscale dimensions are disclosed to be achievable by that process. Where the compound degrades to form a deposit of a metallic or other conductive substance, then the method may be used to manufacture integrated circuits directly on a substrate. The deposit is taught to be, preferably, a metal or metal alloy, and the metals may be gold, tin or chromium, or the deposit may be a conductive non-metal or semi-metal, such as germanium. In a further aspect, there is provided a method for manufacturing an integrated circuit comprising applying to a substrate a compound which degrades under the effect of a radiant or particle beam to produce a conductive, preferably metallic, deposit, applying to selected surface areas of the compound a radiant or particle beam, and removing the degraded compound and the unaffected compound from the substrate.
The processes of the present invention can provide a patterned hard mask, thus replacing both the oxide and photoresist layers used in conventional TSI and ion implantation methods and, for example, simplifying those methods by reducing the number of processing steps which must be performed. Another advantage of this invention is that the material which is produced has better etch resistance to plasma etching chemistries. This confers still another advantage to the present process that allows for the use of extremely thin films as the hard mask, increasing the ultimate resolution of the lithographic process and allowing the formation of smaller and finer features. A further advantage of this invention is that the material which is produced has better ion implant blocking and stopping power. Additionally, the process of the present invention is advantageous in that it facilitates the use of new materials for patterned layers, such as platinum, iridium, iridium oxide, ruthenium and ruthenium oxide, that are known in the art to be difficult or impossible to etch by conventional processes.
In semiconductor processes it is not always possible to run a process continuously due to equipment failures, downtime due to weekends or other non-operational time, and other unexpected occurrences could delay the processing of a deposited film. During the time a deposited film is awaiting processing, the film is subjected to atmospheric conditions such that the humidity in the air may react with the deposited film, which is not preferable for a number of reason such as loss of viable reaction product and possible inconsistencies in the resulting film. Accordingly, it is preferable that a precursor film be hydrolytically stable to avoid the loss of product due to reactions with water in the air. Moreover, semiconductor processes are continuously striving to reduce the throughput time, increase the output and minimize the process cost. Accordingly, it is also preferable to a process to minimize the reaction time and energy used to convert a precursor film, resulting in a metal or metal oxide film. Titanium oxide films have been shown to be effective coatings in many applications in the semiconductor field and otherwise. Thin films of titanium oxide can be used for the production of semiconductors, magnetic film, electrochemical sensors, electro-optical devices, catalysts, ion exchange devices as well as the production of abrasion and corrosion resistant coatings. Uses and benefits of titanium oxide films are described in, for example, U.S. Pat. No. 5,766,784 to Baskaran et al and the references cited therein. However, the Baskaran patent describes a chemical process that is not practical at small scales, such as those used in semiconductor processing. In addition, the patent describes an immersion coating process, which is non-specific and is not useful for processes where patterning is used or coating in only particular areas. A particular titanium ligand pair has been found to exhibit both hydrolytic stability and photosensitivity such that the use of the particular pairing offers significant process benefits in the form of increased throughput, energy efficiency, and decreased lost product due to instabilities at atmospheric.